1. Field of the Invention
This invention pertains to sheet feeding apparatus and methods for operating the same, and particularly to sheet feeding apparatus for feeding sheets from the top of a stack using a rotating vacuum wheel.
2. Prior Art and Other Considerations
Rotating vacuum wheels have long been used to feed sheets from the top of a stack of sheets. Conventional rotating vacuum wheels are essentially disc-shaped and are driven to rotate about the central axis of the disc. A plurality of ports are provided at angular intervals along the circumferential surface of the disc. Each circumferential port communicates through passages in the interior of the disc with one or more corresponding side ports provided on a flat side surface of the disc. Since the vacuum wheel is mounted above the stack of sheets, means are provided for elevating the top of stack into close proximity with the circumference of the wheel at the point whereat the top of the stack is essentially tangent to the circumferential surface of the wheel.
Vacuum wheels are rotated for the feeding of each sheet. During each rotation of the vacuum wheel, when a circumferential port passes through the point of tangency, its corresponding side port is aligned with a port in a vacuum shoe. Alignment of the side port with the vacuum shoe port communicates a vacuum through the interior passages in the vacuum wheel to at least the corresponding circumferential port which is at the point of tangency, whereby the top sheet on the stack is sucked onto the rotating vacuum wheel circumference. As the vacuum wheel rotates, the vacuum-attracted sheet is advanced in a direction of conveyance toward a downstream processing station, receiving bin, or the like.
Rotating vacuum wheels have been operated both in a "stream" feed mode and a "demand" feed mode. According to prior art practice, during either the stream feed or the demand feed mode the vacuum wheel is rotated with the vacuum being all the time communicated to and through the vacuum wheel. In the stream mode the rotation of the vacuum wheel is controlled so that a predetermined interval consistently occurs between the feeding of consecutive sheets whereby the fed sheets are spaced apart from one another with respect to both time and distance along the direction of conveyance. In the demand mode selective rotation or indexing of the vacuum wheel occurs in response to an external signal whereby the feeding of consecutive sheets need not consistently be at a predetermined interval.
Rotating vacuum wheels have traditionally been used in environments in which essentially uniform sheets are fed from the top of a stack of sheets or in environments in which it is known in advance of feeding how unique sheets comprising the stack are related for grouping purposes to neighboring sheets in the stack. Rotating vacuum wheels have not proved advantageous in environments in which unique sheets are fed from a stack and in which it is not known until after feeding (by reading indicia by the sheet) how a sheet is related for grouping purposes to neighboring sheets in the stack.
In the above regard, many institutions mail financial account statements or billing statements to their numerous customers. Each customers statement may comprise a plurality of sheets, each sheet having unique billing information printed thereon and further bearing an indication to which customer's statement the sheet belongs. The number of sheets comprising the statement generally varies from customer to customer. The plurality of sheets comprising the financial statements are fed from a stack; grouped together; and, then subsequently associated with one or more inserts fed from insert stations to form a set of documents which is stuffed into an envelope. An example of a machine accomplishing such functions is described in U.S. Pat. No. 2,325,455 to Williams, which is incorporated herein by reference. In such a machine, sheets comprising the financial statements are fed from a stack or hopper in which the sheets comprising a first customer's statement are consecutively arranged and followed by the consecutive sheets comprising a second customer's statement, and so on with regard to further customers.
When sheets comprising a financial statement are fed and subsequently read to determine to what customer (i.e. group) they belong, there is no way to determine how many sheets comprise a customer's statement until a sheet comprising a subsequent customer's statement is fed and read. In such a situation, the sheet feeder must be controlled so that, once a subsequent customer's first sheet is fed, no further sheets belonging to the subsequent customer are fed until the sheets comprising the previous customer's statement have been properly grouped downstream. Therefore, the feeder must be responsive to control signals so that feeding can be promptly stopped and started, but responsive in a manner whereby the repeated stopping and starting of feeding does not interfere with a desired high rate of sheet feed required for optimum production.
Conventional rotating vacuum wheels have not proven effective in demand mode environments such as that described above. After each sheet is fed, the feeder must be stopped so that a reader can determine whether the just-fed sheet belongs with the previous customer's statement or whether it begins a subsequent customer's statement. Factors including momentum changes involved in the repeated starting and stopping of the rotational motion of a rotating vacuum wheel significantly slow down the feeding operation and greatly hamper production.
In view of the foregoing, it is an object of this invention to provide an efficient rotating vacuum wheel-type feeder and a method of operating the same.
An advantage of this invention is the provision of a rotating vacuum wheel feeder and method of operating the same which enables feeding at a rate of approximately twenty thousand sheets per hour.
A further advantage of this invention is the provision of a rotating vacuum wheel feeder and method of operating the same in which vacuum attraction is properly created for reducing the occurrence of "misses" and/or "doubles".
Yet another advantage of this invention is the provision of a feeding apparatus and method of operating the same wherein sheets are fed at a high rate of speed from the top of a stack for transport to an insertion machine.